Networks, such as using Dense Wave Division Multiplexing (DWDM), Optical Transport Network (OTN), Ethernet, Multiprotocol Label Switching (MPLS and MPLS-Transport Profile (TP)), and the like, are deploying control plane systems and methods. Control planes provide an automatic allocation of network resources in an end-to-end manner. Exemplary control planes may include Automatically Switched Optical Network (ASON) as defined in ITU-T G.8080/Y.1304, Architecture for the automatically switched optical network (ASON) (February 2012), the contents of which are herein incorporated by reference; Generalized Multi-Protocol Label Switching (GMPLS) Architecture as defined in IETF Request for Comments (RFC): 3945 (October 2004) and the like, the contents of which are herein incorporated by reference; Optical Signaling and Routing Protocol (OSRP) from Ciena Corporation which is an optical signaling and routing protocol similar to Private Network-to-Network Interface (PNNI) and Multi-Protocol Label Switching (MPLS); or any other type control plane for controlling network elements at multiple layers, and establishing connections among nodes. Control planes are configured to establish end-to-end signaled connections such as Subnetwork Connections (SNCs) in ASON or OSRP and Label Switched Paths (LSPs) in GMPLS and MPLS. Note, as described herein, SNCs and LSPs can generally be referred to as services or calls in the control plane. Control planes use the available paths to route the services and program the underlying hardware accordingly.
In addition to control planes which are distributed, a centralized method of control exists with Software Defined Networking (SDN) which utilizes a centralized controller. SDN is an emerging framework which includes a centralized control plane decoupled from the data plane. SDN provides the management of network services through abstraction of lower-level functionality. This is done by decoupling the system that makes decisions about where traffic is sent (the control plane) from the underlying systems that forward traffic to the selected destination (the data plane). Examples of SDN include OpenFlow (www.opennetworking.org/sdn-resources/onf-specifications/openflow/), General Switch Management Protocol (GSMP) defined in RFC 3294 (June 2002), and Forwarding and Control Element Separation (ForCES) defined in RFC 5810 (March 2010), the contents of all are incorporated by reference herein. Note, distributed control planes can be used in conjunction with centralized controllers in a hybrid deployment.
Restoration (also referred to as protection) is a key feature in networks where a backup (protection) path takes over for an active (working) path of a service or call when there is a failure in the active path. In particular, one mechanism for protection includes mesh restoration where services are released subsequent to a fault and rerouted, i.e., a new path is computed and the service is rerouted. In conventional implementations, different services are assigned different priorities (e.g., low or high, or even multiple stages priority) and higher priority services are released first to give them the first opportunity to reroute. The lower priority services are conventionally released after a delay based on a fixed timer, e.g., 5 sec. As described herein, the priority can be referred to as high or higher and low or lower and those of ordinary skill in the art will appreciate that a high or higher priority service is one that has a greater level of priority than a low or lower priority service. Specifically, these terms high or higher and low or lower are relative to one another.
Disadvantageously, delaying mesh restoration of low priority services by a fixed amount of time may unnecessarily hold back these services from being restored, e.g., if the timer is 5 sec. and all high priority services mesh restore in 1 sec. then the low priority services are unnecessarily held back for 4 sec., i.e., suffer 4 sec. longer traffic outage than is necessary. The amount of time to hold back mesh restoration for low priority services, or equivalently how much time to allow the high priority services to mesh restore first, is an engineering exercise. This exercise depends on i) the number of nodes and links in the network, ii) how far from source node(s) of the services the failure occurs, iii) the proportion of low priority services to high priority services that fail, and iv) the bandwidth utilization of the network, and other factors. Accordingly, a very conservative number is usually chosen for the hold off timer such as 5 sec., and usually high priority services can mesh restore significantly before the 5 sec. timer expires.
Ideally, the low priority services should be triggered to mesh restore as soon as the high priority services finish. Note that “as soon as all High Priority SNCs finish mesh restoration” includes the cases when high priority services cannot mesh restore due to the network's inability to meet their constraints, i.e., mesh restoration of low priority services should be triggered even if some high priority services cannot be mesh restored, but only once the network determines it cannot satisfy their constraints.